The typical water cooler is in the form of a tower and operates solely by latent cooling in which a portion of the water is evaporated by flowing ambient air either over or through the water. The evaporation process will extract approximately 1000 b.t.u's per pound of water evaporated so that the lowest (final) water temperature which can be obtained is limited by the wet bulb temperature of the air in which the evaporation process is taking place. Thus in common practice, the amount of water consumed in the evaporation process and the lowest temperature obtained by the evaporating water is a function of the ambient conditions under which the process is taking place and is governed solely by the wet bulb temperature of the ambient air.
This invention offers a significant improvement over the system above described, enabling the processed water to be brought to a lower final temperature by depressing the wet bulb temperature of the air utilized during the evaporation process.
More specifically, a depressed wet bulb water cooler is provided with heat exchange walls having opposite exposed surfaces defining wet and dry sides. Water from a load (i.e., water to be cooled) is applied across the wet side surfaces so as to provide extended films of water thereon. Ambient air is flowed into thermal conductive contact with the dry side surfaces thereby cooling the air. The thus cooled air is then used as the working air. It is brought directly to the wet side so that it is applied to the wet side at substantially the temperature to which it was cooled. The cool air flows over the wet side, evaporating portions of water on the wet side surfaces, thereby moistening the air, cooling the water and cooling the wet and dry side surfaces. The moistened air is discharged and cooled water is recovered from the wet side.
By using dry (sensibly) cooled air as the working air, a lower wet bulb temperature is achieved than would be otherwise obtainable if the air were merely drawn upwardly through the hollow conduits directly from the outside.
In particular embodiments the heat exchange walls are formed as an array of elongated, vertically directed conduits. Headers are provided on opposite sides of the conduit array to isolate the spaces between the conduits. The headers facilitate application of the load water at the top entrance apertures of the conduits for flowing therethrough by the force of gravity, while the working air is flowed countercurrently to the water flow.
In a further embodiment, means are provided for pre-cooling of the water used during the evaporation process. Not only does this enhance the ability of the cooler to achieve a lower water temperature, but by the removal of heat from the water prior to the evaporation process, less water is evaporated thereby conserving water. Pre-cooling is accomplished by flowing the working air in thermal conductive contact with a secondary heat exchanger through which the water is flowing prior to its being used in the evaporation process.